MIMO stands for Multi-Input Multi-Output. MIMO is a scheme that adopts a multi-transmission antenna and a multi-reception antenna rather than using a single transmission antenna and a single reception antenna, thereby enhancing data transmission/reception efficiency. That is, this is a technology to increase capacity or enhance performance by using a multi-antenna at a transmission end or reception end in the wireless communication system. MIMO is herein referred to as “multi-antenna”.
In sum, the multi-antenna technology is an application of a technology that, in receiving an overall message, gathers data pieces received from a number of antennas to thereby complete the whole data rather than depending on a single antenna. MIMO may enhance data transmission speed in a specific range or may increase a system range with a specific data transmission speed, and thus, draws attention as a next-generation technology that may overcome a limitation on the amount of transmission in mobile communication due to expansion of data communication, as well as that may be widely used in mobile terminals and relays.
In general, if another version or replica of a transmission signal is not additionally transmitted when the transmission channel is in the situation of deep fading, the transmitter is troubled in determining the transmitted signal. The source corresponding to the other version or replica signal which has been just mentioned is referred to as diversity, which is one of the most critical factors that contribute to reliable transmission over the wireless channel.
Use of diversity may maximize transmission reliability or data transmission capacity. The system that performs diversity by using a multi-transmission antenna and a multi-reception antenna is referred to as “MIMO (Multi Input Multi Output) system” or “multi-antenna system”.
As such, there have been lots of research efforts on spatial diversity schemes using a multi-transmission/reception antenna (MIMO) system to overcome performance deterioration due to channel padding of wireless communication.
The multi-transmission/reception antenna system implements two or more antennas in the transmitter and receiver to thereby provide advantages, such as high data transmission rate, low error rate, and increase in channel capacity.
However, despite such advantages of the multi-transmission/reception antenna, limitations on size, weight, and hardware complexity, generally cause it impossible to implement a multi-transmission/reception antenna system for uplink.
As an alternative to this, the cooperative diversity scheme has been suggested, which aims to allow each terminal in a wireless communication network to obtain advantages, such as spatial diversity gain of a multi-transmission/reception antenna system, decreased error rate, and increased channel capacity, even with at least one or more antennas alone. For this, the cooperative diversity scheme forms a virtual multi-transmission/reception antenna (virtual MIMO) system by allowing nearby terminals to share resources, such as antennas or frequency bandwidths, of relays or relays with femto-cells, so that such advantages of the multi-transmission/reception antenna system may be also achieved by terminals having at least one or more antennas.
As such, the cooperative diversity scheme is based on using a separate relay.
However, there is a need for a method of allowing for cooperative transmission using terminals without a separate relay.